Virtually all locking devices are subject to tampering, possibly resulting from loss of keys, duplication of keys, picking, etc. Furthermore, in many instances, locks are exposed to the environment and, as a result, can become contaminated or corroded. This leads to problems with the proper functioning of the lock which, in turn, results in the need for the lock to be replaced. An example of locks which are subject to these problems are barrel locks of the type conventionally used to secure utility meter boxes against tampering. Such barrel locks effect locking and unlocking by projecting and withdrawing small detent balls through recesses in a barrel-shaped body member of the lock via axial reciprocation of an internal plunger member. Examples of such locks can be found in Moberg, U.S. Pat. Nos. 3,033,016 and 4,015,456.
An example of one attempt that has been made to deal with the problems of tampering and contamination of barrel locks can be seen with reference to Skarzynski, et al., U.S. Pat. No. 4,107,959. The Skarzynski, et al. patent discloses a meter guard lock wherein the box is locked through the use of a conventional barrel lock which is inserted into its locking position through a locking tube. In order to protect the lock from dirt and weather, a plastic plug is inserted into the top end of the locking tube after the barrel lock has been secured in place. Furthermore, in order to deter tampering and efforts to pick the barrel lock, a conventional wire seal is threaded through a pair of diametrically opposed slots in the upper end of the locking tube and through a corresponding slot formed in the plastic plug. A comparable effort along these lines is also disclosed in Swisher, U.S. Pat. No. 4,262,946, wherein a non-removable plug is installed in the top end of the locking tube after the barrel lock has been secured in place, which plug cannot be removed without the plug being destroyed. However, the effectiveness of this approach is limited to the extent that a positive physical indication of tampering will be sufficient to discourage tampering with the lock. Furthermore, the use of such plugs is limited in applicability to barrel lock type locks and plugs are not feasible to use in locks that are required to be frequently locked and unlocked.
Many types of locking devices which are magnetically actuated or controlled are known. In most cases, these devices mimic conventional key-operated tumbler locks in design and operation, and thus suffer from the same types of drawbacks, e.g., they are easily picked and may become disabled from foreign matter entering into the key slot or from moisture-produced corrosion. However, magnetically operated locking devices are known, such as those of Miller, U.S. Pat. No. 4,022,038, and Hallmann, U.S. Pat. No. 3,782,147, that have a lock body and a magnet or a magnet carrying lock member that is displaceably positioned enclosed within an interior space of the body. In both of these patents, the locking device is operated by a key which is seated on a closed key seat (as opposed to within an open key slot) and magnets carried by the key, when properly aligned with the magnets within the lock body, cause a displacement of the internal magnets from a position securing a rotor shaft against rotation (locked position) into a position freeing the rotor shaft for rotational movement (unlocked position) via either the repulsive forces of the aligned magnets (Miller patent) or the attractive forces therebetween (Hallman patent). However, magnetic locks of these types are not readily adaptable to locks such as barrel locks which require axial shifting of a plunger as the means for triggering locking and unlocking, and the number of possible keying combinations is limited by the number of polarity variations for the given number of magnets used, on the one hand, while not being amenable to master keying, where such may be desirable, on the other hand.
Thus, there is a need for a magnetic lock that will be of a pickproof and weatherproof construction, but also have applicability to a wide range of lock types. Furthermore, it is needed to achieve a magnetic lock that not only provides virtually limitless combinations, but also is amenable to master keying.